A technique is known for creating a transgenic plant transformed with DNA sequences comprising a gene coding for a desired protein capable of being expressed in a plant and a certain promoter sequence in order to express that protein. One of such promoters is the cauliflower mosaic virus (CaMV) 35S promoter capable of allowing non-tissue-specific expression of a desired protein in a plant. As regards protein expression systems in plants, inducible gene promoters capable of reacting with an exogenous chemical substance have also been reported, for example a system in which the tetracycline-inducible Tn10 Tet repressor is utilized (The Plant J. (2), 397, 1992) and a system in which the steroid hormone-inducible rat glucocorticoid receptor is utilized (The Plant J. (11), 605, 1997). As regards base sequences involved in tissue-specific expression of plant genes, the so-called RY core sequence CATGCAT associated with a gene that is expressed in a seed-specific manner is known (Plant Physiol. (98), 387, 1992). It has also been disclosed that a desired protein can be expressed in raspberry fruit by using the raspberry drul promoter (Japanese Kohyo Publication 2000-503848).
Cucumisin, a plant-derived protease, is a thermostable alkaline serine protease which is abundantly accumulated in melon juice (Agric. Biol. Chem. (53), 1009, 1989) and cDNA therefor has been cloned (J. Biol. Chem. (52), 32725, 1994)). However, the regulating mechanisms of its fruit-specific expression remain unknown.
Transgenic crop plants transformed with a herbicide resistance gene or the like by utilizing the technology of introducing a heterologous DNA into plants to create transgenic plants have already been utilized in food production. On the other hand, another method of utilizing transgenic plants, namely the development into the so-called molecular agriculture in which plants are caused to produce useful proteins and the products are extracted for utilization, cannot yet be said to have been established as an industry. When plant cells are or a plant body is caused to produce a useful protein or a useful substance resulting from conversion thereof, there arise the possibility that if the product is expressed in the leaf, stem or root, the extraction efficiency or purification/recovery of the product may become or encounter problems in some not only in the case of non-tissue-specific expression in a plant but also in the case of specific expression. A promoter readily controllable and ensuring good production efficiency is thus desired. The fruit is a storage organ by far greater in volume than seeds and, in particular, the gourd family, typically melon, is characterized by its producing a great number of relatively large fruits. If a technology of accumulating a useful protein or useful substance in those fruits or giving them desired properties is established, the technology will become a very useful one. While there are several reports about the base sequences involved in expression specific to the seed, leaf or root of plants, there is no report found about the identification and utilization of a base sequence, in particular a melon promoter sequence, involved in fruit-specific expression.